In U.S. Pat. No. 4,909,579 issued Mar. 20, 1990 assigned to the same applicant and entitled "CASING FOR CONSOLE (CPU) OF PERSONAL COMPUTER WITH EASY OPENING AND LOCKING MEANS", there is disclosed a mechanism for achieving the function of easy opening and locking of the cover body and the base by having the locking tabs provided on both sides of the cover body be securely fitted into the notches on both sides of the base in combination with slide rods pivotally coupled between the cover body and the base. In addition, in U.S. Pat. No. 5,123,680 issued Jun. 23, 1992 assigned to the same Applicant and entitled "FASTENING DEVICE FOR CONNECTING THE FRONT PANEL TO A COMPUTER CASING", there is disclosed a plurality of retaining elements secured to the front panel of a computer casing which are provided with a plurality of resilient locating legs such that the retaining elements can be positioned, along with the front panel, on the base by means of the returning force of said resilient locating legs after which have been inserted into retaining holes previously provided on the base.
According to the basic concept of the non-screw assembled casing for computer mainframe of the present invention, the upper cover is positioned on the base in the X-axis (vertical) direction and Y-axis (lateral) direction by means of a first coupling section structure and a second coupling section structure provided on the inner side of the upper cover and on both sides of the base, and in the Z-axis (longitudinal) direction by means of the third coupling section structure provided on the back side of the front panel, the periphery of the front side of the upper cover, and the front side of the base. As shown in the embodiment given in the present application, the first fastening units provided in the first coupling section structure and the second fastening units provided in the second coupling section structure are similar to the locking tab and notch fitting structure of the aforesaid ROC Patent Application No. 77208217, and the third fastening units provided in the third coupling section structure are similar to the resilient retaining elements of ROC Patent Application No. 79210388. The structure of the fastening units of the present invention is not limited to the above structure of elements. Rather, the present invention has its emphasis placed on that the upper cover and the base can be secured in the directions of the X-, Y-, and Z-axes without requiring fastening by screws. Therefore, the present invention provides a concept of securing the upper cover and the base in the directions of the X-, Y-, and Z-axes at the same time in a manner which has not yet been found in any prior art.